1. Field of the Invention
The present invention relates to optical switching devices and more particularly to optical switching devices that exhibit low crosstalk characteristics between switchable channels.
2. Description of the Prior Art
Advances in the optical communications art have generated a need for devices that are capable of switching optical signals from one signal channel to another. Some of the devices that have been developed that are capable of performing this switching function employ Bragg diffraction from launched surface acoustic waves, Bragg diffraction by dielectric gratings created by voltage controlled fringing electric fields in an optical guide made of electro-optic high resistivity solid state material, and optical directional couplers wherein coupling from one optical channel to the other is electrically controlled. Each of these are four port devices wherein beam direction or optical waveguide coupling is altered upon the application of an external electrical control signal, and may be employed as switches per se or as elemental switches in a permutation array which couples a signal at one of n input ports to one of n output ports.
Permutation arrays of the prior art focus the attention to the elimination of waveguide crossovers and to the minimization of the number of element switches required to effect the coupling of the n input ports to the n output ports thus providing an array that is relatively easy to fabricate and wherein each port of each element switch is utilized. In these arrays, a crosstalk (leakage) signal from each elemental switch is transported through the array arriving at the output ports as an intefering signal with the desired signal thereat. To hold the inter-channel crosstalk to tolerable levels, generally requires that the elemental switches be fabricated to tolerances that may not be achievable or are too costly.
The present invention discloses an optical switch that is relatively inexpensive to fabricate and when utilized in a switching array significantly reduces the output crosstalk relative to that of the prior art permutation arrays.